Exit signs are located in theaters, public buildings, high-rise apartment buildings, and the like for purposes of guiding people safely to exit stairways and exit doorways and the like from these such structures in times of emergency. Normally, they use incandescent lamps which generate large amounts of heat thereby shortening the life of the light source and requiring considerable maintenance and expense. Moreover, since these exit signs are located in buildings which require that they be on in times of emergency and highly visible, possibly through smoke and haze, they require a backup electrical power source in the event of failure of the main power line, such as a conventional 110 volt main. Such prior art systems also may require the alternative lamps or low-voltage lamps which turn on in the event of failure of the main power supply. See FIG. 1 and U.S. Pat. Nos. 5,611,163 and 5,526,251. There have been efforts to incorporate fluorescent lamps into exit signs. See U.S. Pat. Nos. 4,587,600 and 4,650,265 as examples.
The object of the invention is to provide a new and improved ballastless, non-thermionic and starterless fluorescent exit sign which works on inducing oscillation on the gas contained in the tube at a frequency which is related to the type of gas to obtain maximum luminosity without the presence of a carrier, consumes little electrical energy (2.6 watts) and which is dimmable without flickering regardless of the level of luminosity and in which the light spectrum is constant.
Another object of the invention is to provide an improved exit sign which is low in cost and low in energy consumption.
The exit sign of the present invention incorporates a ballast- free, starter-free, non-thermionic conventional fluorescent lamp or tube driven by a high-frequency square wave driver circuit.
Another object of the invention is to provide a low voltage (under 85-90 volts), non-thermionic, ballast-free, fluorescent lighting system for exit signs.
According to the invention at least one gas discharge lighting lamp or tube (which may be constituted by UV-responsive phosphor-coated envelope confining a gaseous discharge medium at a predetermined pressure between a pair of electrodes) is mounted in an "exit" sign housing and non-thermionically driven by a low-voltage square wave power supply. The square wave power supply may incorporate a solid state switch which is operated to generate a substantially square wave alternating current wave at the lamp or tube electrodes such that the voltage supplied to the electrodes reverses polarity more rapidly than the pattern of electron and ion density in the tube can shift so that electrons throughout the length of the tube are continually accelerated and will, through several cycles of said square wave, create free electrons and ions throughout the tube's volume, in steady state operation and illuminate the fluorescent lighting ifs lamp. The frequency of oscillation is preferably related to the type of gas to obtain maximum luminosity without the presence of a carrier. The current in the tube is minimal and no noticeable level of RFs are present, that is, there is substantially no radio interference.
The oscillating transformer in the present invention provides a level of luminosity which is a function of the voltage thereby making dimming of the fluorescent lamp possible without flickering (90% dimming) regardless of the level of luminosity. The band on the spectrum is constant and reflects the initial reaction to the oscillation. The system works in any type of gas filled envelope.
Thus, there is disclosed a sign lighting system comprising a housing having signage indicia in a wall thereof. A fluorescent gas discharge lamp is mounted inside the housing and a source of low-voltage high-frequency square wave voltage having a pair of output terminals and an LC-free circuit connecting the low-voltage, high-frequency, square wave voltage to the fluorescent gas discharge lamp to non-thermionically excite the fluorescent gas discharge lamp and thereby illuminate the translucent member and the indicia formed in the wall of the housing.
In a preferred exit sign system, a 7.2 volt DC rechargeable battery is used. The battery backup has a battery charging circuit and uses a 7.2 volt nicad rechargeable battery. The fluorescent tube is an FT6 fluorescent tube with no starter or ballast and the filaments are not connected to a source of heater current. The light output in such a lamp is bright and the battery good for three hours (when only ninety minutes are required by federal regulations). The exit sign uses 2.6 watts of energy (in comparison to the standard sign on the market uses 50 watts). The display is green which corresponds to the new spec for LED equipped signs in the market which are only red. The cost of manufacturing is much lower than the standard sign on the market.
In one preferred embodiment, the driver circuit of the present invention includes an oscillating transformer having a primary and secondary winding with the primary winding center tapped and coupled to the toggle or gate electrode of a switching diode. A supply of direct current such as a low-voltage battery is applied through a electrolytic filter capacitor and a 1500 ohm resistor bypassed by a capacitor. A third capacitor shunts the switching diode. The circuit operates to provide 3.9 megahertz square waves output on the secondary at 1.4 volts to a fluorescent tube such as FT6. An AC supply is rectified and used to supply the driver circuit.
A charging circuit for a battery is connected to the AC supply. Upon failure of the AC supply, the battery automatically supplies DC voltage to the driver circuit.